Schema validation

Here's the Cerberus validation schema for the config file:

shares:
  type: list
  required: True
  empty: False
  schema:
    type: dict
    required: True
    schema:
      name:
        type: string
        required: True
      symbol:
        type: string
        required: True
      purchase:
        type: dict
        required: True
        schema:
          quantity:
            type: number
            required: True
            min: 0
          fee:
            type: number
            required: True
            min: 0
          cost_price:
            type: number
            required: True
            min: 0
      estate:
        type: dict
        required: True
        schema:
          quantity:
            type: number
            required: True
            min: 0
          received_dividend:
            type: number
            required: True
            min: 0